Active matrix type liquid crystal display apparatus

ABSTRACT

A liquid crystal display apparatus having a liquid crystal panel including a pair of substrates, a plurality of electrodes formed on at least one of the pair of substrates and a liquid crystal layer sandwiched between the pair of substrates, and a light source provided on one surface of the liquid crystal panel. An electric field in the liquid crystal layer produced by the plurality of electrodes is predominantly in parallel with surfaces of the pair of substrates. The light source has a luminous characteristic with a first chromaticity and the liquid crystal panel has a characteristic of spectral transmittance with a second chromaticity different from the first chromaticity so as to compensate for the color of the light source.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This is a continuation of U.S. application Ser. No. 09/572,375,filed May 18, 2000, which is a continuation of U.S. application Ser. No.08/740,008, filed Oct. 23, 1996, the subject matter of which isincorporated by reference herein.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to a liquid crystal displayapparatus, and, more particularly, to an active matrix liquid crystaldisplay apparatus.

[0003] Various examples of liquid crystal display apparatus aredisclosed, for example, in Japanese Patent Publication No. 63-21907(1988), UP, WO91/10936 and Japanese Patent Application Laid-Open No.6-222397 (1994), in which a pair of comb electrodes are used to apply anelectric field to a liquid crystal in a direction parallel to thesurface of a substrate. However, in a display system of this typewherein the direction of an electric field applied to the liquid crystalis controlled to be parallel with the surface of a substrate by usingactive elements (hereinafter referred to as a horizontal electric fieldtype), no consideration is given to the characteristic of the lightsource required to decrease the power consumption of the whole liquidcrystal display apparatus. Further, no consideration is given to theconfiguration of the liquid crystal display apparatus required tosuppress color shift in response to the application of a voltage theretoand to prevent a color defect from occurring.

[0004] In the establishment of a horizontal electric field, opaqueelectrodes are provided in a display pixel portion in order to producean electric field substantially in parallel with the surface of thesubstrate. As compared with the prior art type of display panel whereinan electric field is applied in a direction substantially vertical tothe surface of the substrate by using a transparent electrode, theaperture ratio may be deteriorated and the brightness under a brightstate may be reduced. Accordingly, it is necessary to use ahigh-intensity light source in the horizontal electric field producingtype of display panel.

[0005] Because the display mode effective for a liquid crystal displayapparatus of the horizontal electric field type is a double refractionmode, the transmittance T can be generally expressed by the followingequation (1): $\begin{matrix}{T = {{To}\quad \sin^{2}2\quad {\theta \cdot {\sin^{2}\left( \frac{{nd}\quad \Delta \quad n}{\lambda} \right)}}}} & (1)\end{matrix}$

[0006] where, To designates a coefficient and is determined mainly bythe transmittance of the polarizer used in the liquid crystal panel, θdesignates the angle between an effective optical axis in the liquidcrystal layer and a transmittance axis for polarized light, d designatesthe thickness of the liquid crystal layer, Δn designates the anisotropyof the refractive index of the liquid crystal layer, and λ denotes thewavelength of light. Because the transmittance of the liquid crystaldisplay apparatus has essentially a maximum value at a certainwavelength, the liquid crystal display elements are colored. Onesolution to the above equation is a value which satisfies a conditionwherein the peak wavelength becomes equal to the maximum wavelength 555nm for luminous efficiency under a retardation of 0 order, that is,(πd·Δn/555)=π/2. In this case, the transmittance falls suddenly on theshort wavelength side of the peak wavelength, and it decreases graduallyon the long wavelength side. Therefore, the liquid crystal displayelements are colored yellow. As a result, it is required to use a lightsource with the color of a cold color family which represents acomplementary color to yellow. In other words, it is required to use alight source with a high color-temperature characteristic.

[0007] In general, a fluorescent lamp is used as a light source for aliquid crystal display apparatus. Because the luminous efficiency of thefluorescent lamp in a short wavelength region is less than that in along wavelength region, the brightness may be reduced, and so a largeconsumption of power is required to obtain a high brightness. Since thenormal voltage of the battery must be maintained for a long time, forexample, in a note book type personal computer or personal digitalassistance, it is required to avoid any increase in the powerconsumption.

[0008] Now, the display operation of a liquid crystal display apparatusof the horizontal electric field type can be obtained in the doublerefraction mode, and the transmittance T can be generally expressed bythe following equation (2):

T=T ₀·sin²2θsin²[(π·d _(eff) ·Δn)/λ]  (2)

[0009] where, _(To) designates a coefficient and is determined mainly bythe transmittance of the polarizer used in the liquid crystal panel, θdesignates the angle between an effective optical axis in the liquidcrystal layer and a transmittance axis for polarized light, d_(eff)designates the thickness of the liquid crystal layer, Δ denotes theanisotropy of the refractive index of the liquid crystal layer, and λdesignates the wavelength of light. Further, the product of d_(eff) andΔ is referred to as retardation. Here, the thickness d_(eff) of theliquid crystal layer is not the thickness of the whole liquid crystallayer, but the thickness of the liquid crystal layer in which thedirection of alignment is changed when a voltage is applied.

[0010] In general, the molecules of the liquid crystal in the vicinityof the boundary surface of a liquid crystal layer do not change thealignment direction due to the effect of anchoring at the boundarysurface even if a voltage is applied. Accordingly, when the thickness ofthe whole liquid crystal layer sandwiched between the substrates equalsd_(eff), d_(eff) <d_(LC) always is maintained between the thicknessd_(LC) and d_(eff). It is estimated that the difference between d_(LC)and d_(eff) equals about 20 nm to 40 nm.

[0011] As clearly seen from the above equation (2), the transmittance ofthe liquid crystal display panel takes a maximum value at a specificwavelength (peak wavelength). Therefore, the liquid crystal displayelement is easily colored, in other words, it is easy to beunnecessarily colored.

[0012] Generally, the liquid crystal panel is constructed so that thepeak wavelength may become equal to the maximum wavelength 555 nm forluminous efficiency, that is, (πd·Δn/555)=π/2. At this time, the liquidcrystal display element is colored yellow, because the spectraltransmittance falls suddenly on the short wavelength side of the peakwavelength, and it decreases gradually on the long wavelength side.

[0013] The extent of coloring extremely changes with the application ofa voltage to the liquid crystal. As the magnitude of the voltage valuechanges from the minimum voltage required for display to the medium tonedisplay voltage and then to the maximum voltage, the color tone isgradually changed. Therefore, the display state of colors is extremelydeteriorated.

[0014] Because the difference between the thickness of the liquidcrystal layers appears as a change in the peak wavelength in thebirefringence mode, the local and abnormal thickness of the liquidcrystal display layer causes display defects, such as variations in theintensity and/or color tone, which are different from those in itssurrounding area.

SUMMARY OF THE INVENTION

[0015] An object of the present invention is to provide an improvedliquid crystal display apparatus, in which a low power consumption and afine display characteristic are compatible with each other.

[0016] Another object of the present invention is to provide an improvedliquid crystal display apparatus which can suppress color shift causedby the application of a voltage and reduce the occurrence of a colordefect due to a local difference in thickness in the liquid crystallayer.

[0017] A liquid crystal display apparatus according to the presentinvention comprises a liquid crystal panel having a pair of substrates,a plurality of electrodes formed on at least one of said pair ofelectrodes and a liquid crystal layer sandwiched between said pair ofsubstrates, and a light source provided on one surface of said liquidcrystal panel. The light source has a luminous characteristic with thechromaticity of a warm color family and said liquid crystal panel has acharacteristic of spectral transmittance with the chromaticity of a coldcolor family. Thereby, the color of said light source can becompensated.

[0018] The warm color family includes colors with a reddish hue, such asyellow or orange, in contradistinction with “white” illuminated from thestandard illuminant C. The cold color family includes colors with abluish hue in contradistinction with “white” illuminated from thestandard illuminant C. While an illuminant with a color of the warmcolor family has a transmittance which is low at a shorter wavelength,for an illuminant with a color of the cold color family, thetransmittance is low at a longer wavelength. Therefore, by combiningthem, it becomes possible to transmit light almost uniformly in thevisible region. As a result, the display of the whole liquid crystaldisplay apparatus approaches “white”, as illuminated from the standardilluminant C.

[0019] The reason why the power consumption is reduced by using thepresent invention is as follows. The fluorescent lamp with a color ofthe warm color family tends to consume less electric power than one witha color of the cold color family while obtaining the same intensity. Ingeneral, it is assumed that the power consumption of a fluorescent lampwith a color temperature of 6000K is 1, the power consumption requiredto obtain the same intensity results in a 5% increase in a fluorescentlamp with a color temperature of 8000K and a 10% increase in one with atemperature of 10000K, but a 5% decrease in one with a temperature of4000K. For example, in order to compensate the color in a liquid crystaldisplay element colored in yellow, by using a fluorescent lamp with acolor temperature more than the 6770K of the white standard illuminantC, it is necessary to use an illuminant with a color temperature ofpreferably more than 10000K. For example, if an electric power of 2watts is consumed by using a fluorescent lamp with a color temperatureof 8700K in the liquid crystal display apparatus of the horizontalelectric field type, an electric power of 2.06 watts is consumed when afluorescent lamp with a color temperature of 10000K is used. However, ifthe fluorescent lamp with a color temperature of 6000K lower than thatof the white standard illuminant C is used, the power consumption is1.87 watts, and if one with 4000K is used, it becomes 1.79 watts.

[0020] The illuminant with a color of the warm color family may be madeby changing the kind of fluorescent materials being used and theirmixing ratio. A narrow band emission type fluorescent lamp can be madeby mixing the materials selected from each of the following A, B and Cgroups. The A group has an emission peak in the range of 450 nm to 490nm, and includes the following materials:

[0021] 3Ca₃(P0 ₄)₂. Ca(F,C1)₂:3b³⁺, Sr₁₀(PO₄)₆C₁₂:Eu²⁺, (Sr,Ca)₁₀(P0₄)₆C₁₂:Eu²⁺, (Sr, Ca)₁₀(PO₄)₆C₁₂.nB₂O₃:Eu⁺², (Ba, Ca,Mg)₁₀(PO₄)₆C₁₂:EU²⁺, Sr₂P₂Oτ:Sn²⁺, Ba₂P₂τ:Ti⁴⁺, 2SrO.0. 84P₂O₆.).16B₂O₃:Eu²⁺,MgWO₄, BaA₁₈O₁₃:EU²⁺, BaMg₂Al₁₆O₂₇: Eu²⁺Mn²⁺, SrMgAl₁₀O₁₇:Eu²⁺

[0022] The B group has an emission peak in the range of 540 nm to 550nm, and includes the following materials:

[0023] LaPO₄:Ce³⁺, Tb³⁺, LaO₃0.2SiO₂.0.9P₂O₅:Ce³⁺, Tb³⁺, Y₂Sio₅: Ce³⁺,Tb³⁺, CeMgAi₁₁O₁₉:Tb³⁺, CdMgB₅O₁₀:Ce³⁺, Tb³⁺

[0024] The C group has an emission peak in the vicinity of 610 nm, andincludes the following materials:

[0025] (Sr,Mg)₃(PO₄)₂:Sn²⁺, CaSiO₃:Pb²⁺, Mn²⁺, Y₂O₃:Eu³⁺, Y(P,V)O₄:Eu³⁺

[0026] By changing the mixing ratio, it becomes possible to control therelative intensity of each of the emission regions, and thus realize afluorescent lamp with various color temperatures. Further, by increasingthe mixing ratio of the fluorescent materials having an emission peakaround 610 nm, it becomes possible to make a fluorescent lamp with alower color temperature in the warm color family.

[0027] There are three methods to realize a liquid crystal displayapparatus of the cold color family.

[0028] (1) A characteristic of the cold color family can be obtained bypositioning the maximum value of the transmittance in a short wavelengtharea. The luminescence spectrum of the fluorescent materialcorresponding to green resides in the range of 540 nm to 550 nm, andthat corresponding to blue in the range of 450 nm to 490 nm. It is,therefore, possible to obtain a liquid crystal display apparatus of thecold color family when the maximum luminescence spectrum is less than520 nm, that is, when d·Δn=0.26 in the equation (1), because the bluecolor is emphasized in such a case. Here, d denotes the thickness(d_(eff)) of the liquid crystal layer which changes the direction ofalignment when a voltage is applied. The molecules of the liquid crystalin the vicinity of the boundary surface of the liquid crystal layer doesnot change the direction of alignment due to the effect of anchoring ofthe boundary surface even when a voltage is applied. When the thicknessof the liquid crystal layer sandwiched between the substrates is d_(LC),the thickness of the liquid crystal layer which changes the direction ofalignment when a voltage is applied is d_(eff), d_(eff)<d_(LC) and thedifference between d_(eff) and d_(LC) may be about from 300 nm to 400nm.

[0029] (2) The liquid crystal display panel may be provided with abirefringent film, which is set so as that the peak wavelength of thespectrum transmittance in the liquid crystal display panel can be withinthe short wavelength range of the visible light of 400 nm to 520 nm,preferably 440 nm to 490 nm. color filter. The thickness of the liquidcrystal layer at a portion where red light can be transmitted is lessthan the thickness d_(LC) of the liquid crystal layer at a portion wheregreen light or blue light can be transmitted.

[0030] The threshold voltage Ec in the liquid crystal display apparatusis expressed by the following equation: $\begin{matrix}{{Ec} = {\frac{\Pi}{d_{LC}}\sqrt{\frac{K_{2}}{{ɛ0\Delta}\quad ɛ}}}} & (3)\end{matrix}$

[0031] where, d_(LC) designates the thickness of the liquid crystallayer, K₂ represents an elastic constant, Δε designates the anisotropyof a dielectric constant of the liquid crystal, and denotes a dielectricconstant for a vacuum. As d_(LC) is reduced, the threshold voltageshifts to a higher voltage. By setting the thickness of the liquidcrystal to be thin at a pixel portion where red is displayed, it becomespossible to shift red, that is, a voltage-transmittance characteristicin a long wavelength region to a higher voltage side. Thereby, thetransmittance at the long wavelength region for each voltage issuppressed, and thus it becomes possible to make a liquid crystaldisplay apparatus in which the transmittance in the short wavelengthregion is larger. In order to suppress sufficiently the transmittance inthe high wavelength region and hold a color balance, it is preferablethat the change in thickness of the liquid crystal is suppressed withinthe range of 0.1 μm to 1 μm. For example, it is possible to reduced_(LC) by thickening the film at a portion of the color filter where redis displayed. It may be possible to thicken the film at a portion of thecolor filter where blue is displayed more than d_(LC) at portions wherered and green are displayed. Also, in this case, it is preferable thatthe change in the thickness of the liquid crystal layer is within therange of 0.1 μm to 1 μm.

[0032] The illuminant used in accordance with the present invention hasa maximum value of at least one intensity in each range from 400 nm to500 nm, from 500 nm to 600 nm and from 600 nm to 700 nm of said lightsource, and the liquid crystal panel has a characteristic of spectraltransmittance required to satisfy the relation, x>y>z, where x equals avalue of the transmittance at the wavelength which shows the maximumvalue of the intensity in the range from 400 nm to 500 nm, y denotes avalue of the transmittance at the wavelength which shows the maximumvalue of the intensity in the range from 500 nm to 600 nm, and z denotesa value of the transmittance at the wavelength which shows the maximumvalue of the intensity in the range from 600 nm to 700 nm. Thus, it ispossible to suppress the color shift caused by the change in the appliedvoltage and to provide a liquid crystal display apparatus having a finedisplay characteristic.

[0033] The reason why a fine display characteristic can be obtained willbe explained hereinafter.

[0034] As described above, the liquid crystal display apparatus isgenerally operated in a birefringent mode. Its transmittance isexpressed in the equation (2). Accordingly, the liquid crystal displayapparatus has a spectral transmittance which has its maximum value at acertain wavelength, suddenly decreases on the shorter wavelength side,and gradually decreases on the longer wavelength side. It is assumedthat the peak wavelength is around 550 nm. The transmittance suddenlydecreases in the range of 400 nm to 500 nm, which is in a blue region.As the brightness of the liquid crystal panel increases, the dependenceof the transmittance on the wavelength becomes remarkable. Accordingly,this is the factor which causes the color shift according to a change inthe applied voltage.

[0035] When the thickness of the liquid crystal layer at a certainportion is locally different from other portions in the liquid crystaldisplay apparatus, the transmittance of blue at the portion remarkablychanges and a color defect may occur. Accordingly, it should be notedthat it is important to suppress any sudden decrease of thetransmittance in the short wavelength region of the peak wavelength orthe blue region. In order to suppress a sudden decrease of thetransmittance in the short wavelength region, it is effective to shiftthe peak wavelength to the short wavelength side by setting thewavelength λ to be shorter than 550 nm under the condition ofd_(eff)·Δn(λ)=λ/2.

[0036] The more the wavelength λ is spaced from the peak wavelength, themore the extent of the decrease of the transmittance increases. It is,therefore, possible to suppress a sudden decrease of the transmittancein the short wavelength region by setting the peak wavelength to theshorter wavelength side. It is also important to suppress a suddendecrease of the transmittance at the wavelength of emission from theilluminant being used.

[0037] In general, a narrow band emission type fluorescent lamp is usedfor the illuminant of the liquid crystal display apparatus. Such afluorescent lamp uses materials which have a luminescence peak at eachspectrum region of red (R), green (G) and blue (B).

[0038] The following group has an emission peak in the range of 450 nmto 490 nm corresponding to blue, and includes the following materials:

[0039] 3Ca₃(PO₄)₂.Ca(F,C1)₂:3b³⁺, Sr₁₀(PO₄)₆C₁₂:Eu²⁺,(Sr,Ca)₁₀(PO₄)₆C₁₂:Eu²⁺, (Sr, Ca)₁₀(PO₄)₆C₁₂.nB₂O₃:Eu⁺²,(Ba,Ca,Mg)₁₀(PO₄)₆C₁₂:EU²⁺, Sr₂P₂O_(τ):Sn²⁺, Ba₂P₂τ:Ti⁴⁺, 2SrO.0.84P₂O₆.). 16B₂O₃:Eu²⁺, MgWO₄, BaA₁₈O_(l3): Eu²⁺, BaMg₂Al₁₆O₂₇:Eu^(2+Mn)²⁺, SrMgAl₁₀O₁₇:Eu²⁺

[0040] The following group has an emission peak in the range of 540 nmto 550 nm corresponding to green, and includes the following materials:

[0041] LaPO₄:Ce³⁺, Tb³⁺, LaO₃.0.2SiO₂.0. 9P₂O₅:Ce³⁺, Tb³⁺, Y₂SiO₅ :Ce³⁺,Tb³⁺, CeMgAi₁₁O₁₉:Tb³⁺, CdMgB₅O₁₀:Ce³⁺, Tb³⁺

[0042] The following C group has an emission peak in the range of 610 nmto 630 nm corresponding to red, and includes the following materials:

[0043] (Sr,Mg)₃(PO₄)₂:Sn²⁺, CaSiO₃:Pb²⁺, Mn²⁺, Y₂O₃:Eu³⁺, Y(P,V)O₄:Eu³⁺

[0044] The luminescence characteristic of the narrow band emission typefluorescent lamp made with fluorescent materials selected from each ofthe above groups is as follows. The spectrum corresponding to blue iswithin the range of 450 nm to 490 nm, the spectrum corresponding togreen is in the vicinity of 545 nm, and the spectrum corresponding tored is within the range of 610 nm to 630 nm.

[0045] Therefore, the characteristic of the spectrum transmittance whichshould be taken into consideration in the liquid crystal panel using theabove narrow band emission type fluorescent lamp is as follows. Itshould have the range of 450 nm to 490 nm as a blue region, the range inthe vicinity of 545 nm as a green region, and the range of 610 nm to 630nm as a red region.

[0046] Accordingly, the most effective characteristic of thetransmittance to suppress color shift and/or color defects in the liquidcrystal panel has a maximum value in the wavelength region of 450 nm to490 nm. The retardation d_(eff). Δn(λ) should be set to be less than0.245 μm (λ=490 nm) to fit the peak of the transmittance to the abovewavelength region. Further, it is necessary to use a liquid crystalmaterial which has a small anisotropy Δn of refractive index and a thinliquid crystal layer to reduce the retardation d_(eff)·Δn.

[0047] As described above, it is important to fit the characteristic ofthe luminescence at the short wavelength region of the illuminant to thepeak of the transmittance of the liquid crystal panel. Here, thespectral transmittance does not mean the spectral characteristic afterpassing through a color filter, etc., but refers to the characteristicof the transmittance of the liquid crystal panel itself.

[0048] While the peak wavelength of the transmittance may change alittle by using a certain color filter, it is possible to ignore itseffect during actual use. The most important point in accordance withthe present invention resides in the relationship between the peak ofthe intensity of the illuminant and the transmittance of the liquidcrystal panel.

[0049] The magnitude of the anisotropy An of the refractive index of theliquid crystal changes according to temperature. If the temperature ofthe liquid crystal panel changes due to the environment of the placewhere the display apparatus is used, the set value of the retardationd_(eff)·Δn may change.

[0050] In a liquid crystal in which the anisotropy An of the refractiveindex is relatively small, the change in the anisotropy Δn itself of itsrefractive index becomes small. In addition, if the thickness d_(eff) isalso small, the change in the product d_(eff)·Δn of the thickness andthe anisotropy becomes smaller. Accordingly, by using the above liquidcrystal, it is possible to obtain an expansion of the margin of thetemperature, and thus suppress any change in the retardation d_(eff)··n.

BRIEF DESCRIPTION OF THE DRAWINGS

[0051]FIG. 1 is a diagrammatic view of the liquid crystal displayapparatus according to the present invention.

[0052]FIG. 2 is a graph which shows a characteristic of the spectraltransmittance of a liquid crystal display panel of the horizontalelectric field type.

[0053]FIG. 3 is a diagram which shows the definition of a direction ofrubbing and a direction of the axis of a polarizer.

[0054] FIGS. 4(a) and 4(b) are side-sectional views each showing onepixel portion of the liquid crystal display panel of the horizontalelectric field type.

[0055] FIGS. 4(c) and 4(d) are front views of the panels of FIGS. 4(a)and 4(b), respectively, wherein active elements are not shown except agate insulating film 2.

[0056]FIG. 5 is a graph which shows color temperatures and chromaticitycoordinates.

[0057]FIG. 6 is a diagram which shows the configuration of the substrateof a color filter.

[0058] FIGS. 7(a) and 7(b) each show an shows the emissioncharacteristic of an illuminant.

[0059] FIGS. 8(a) and 8(b) each show an the emission characteristic ofan illuminant.

[0060]FIG. 9(a) shows the spectral transmittance of the liquid crystaldisplay panel when a drive voltage is applied.

[0061]FIG. 9(b) shows a luminescence spectrum obtained by using a lightsource.

[0062]FIG. 10 is a graph which shows chromaticity coordinates concerningthe above construction members.

[0063]FIG. 11A shows the spectral transmittance of the liquid crystaldisplay panel when a drive voltage is applied.

[0064]FIG. 11B shows a luminescence spectrum obtained by using a lightsource.

[0065]FIG. 12 is a graph which shows chromaticity coordinates of theliquid crystal display apparatus.

[0066]FIG. 13A shows a luminescence spectrum and 14B shows chromaticitycoordinates concerning the construction members.

[0067]FIG. 14A shows a luminescence spectrum and 14B shows chromaticitycoordinates concerning the construction members.

[0068]FIG. 15 shows a trail appearing on chromaticity coordinates.

[0069]FIG. 16 shows a voltage-transmittance characteristic of the liquidcrystal display apparatus.

[0070]FIG. 17 shows a voltage-transmittance characteristic of the liquidcrystal display apparatus.

[0071]FIG. 18 shows a voltage-transmittance characteristic of the liquidcrystal display apparatus.

[0072]FIG. 19 shows a trail appearing on the chromaticity coordinates.

[0073]FIG. 20 is a cross-sectional view of a liquid crystal displaypanel of the horizontal electric field type, FIG. 20(a) is a view takenalong line A-A′ and FIG. 20(b) is a view taken along line B-B′ in FIG.20.

[0074]FIG. 21 is a cross-sectional view of a liquid crystal displaypanel of the horizontal electric field type, FIG. 21(a) is a view takenalong line A-A′ and FIG. 21(b) is a view taken along line B-B′ in FIG.21.

[0075]FIG. 22 is a diagram of a color filter according to an embodimentof the present invention, FIG. 22(a) is a view taken along line A-A′ andFIG. 22(b) is a view taken along line B-B′ in FIG. 22.

[0076]FIG. 23 is a schematic view of a driving circuit for the liquidcrystal display apparatus.

[0077]FIG. 24 is a diagrammatic view of a color filter according to anembodiment of the present invention.

[0078]FIG. 25 shows an emission spectrum.

[0079]FIG. 26 shows an illustration of spectral transmittance.

[0080]FIG. 27 shows one example of an operating characteristic of adriving circuit for the liquid crystal display apparatus.

[0081]FIG. 28 shows an illustration of spectral transmittance.

[0082]FIG. 29 shows an illustration of color shift.

[0083]FIG. 30 shows an illustration of color shift.

[0084]FIG. 31 shows one example of an operating characteristic of adriving circuit for the liquid crystal display apparatus.

[0085]FIGS. 32 and 33 show the characteristics of the brightness to theapplied voltage in embodiments A and B by setting each of R, G and B asparameters.

[0086]FIGS. 34 and 35 show characteristics similar to those of FIGS. 31and 32 with regard to comparison examples C and D.

[0087]FIG. 36 shows a characteristic of transmittance.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0088] Embodiments of the liquid crystal display apparatus according tothe present invention will be explained hereinafter with reference tothe attached drawings.

[0089] Firstly, the configuration and the principle of operation of aliquid crystal display element of the horizontal electric field typewill be explained with reference to FIG. 3, which illustrates thedefinition of the direction of rubbing and the direction of the axis ofa polarizer.

[0090] In FIG. 3, reference numeral 1 designates a common electrode, 4designates a pixel electrode, 9 designates the direction of an electricfield, 10 denotes a longitudinal axis (optical axis) of a molecule ofthe liquid crystal, and 11 denotes the transmitting axis of polarizedlight. Further, ΦP designates an angle between the transmitting axis 11and a polarizer 8 (see FIG. 1), and ΦLC designates an angle between thedirection 9 of the electric field and the optical axis 10 in thevicinity of a boundary surface.

[0091] Because there are a pair of polarizers and a pair of boundarysurfaces, respectively, an upper one and a lower one, the relevantangles are expressed as ΦP1, ΦP2, ΦLC1, and ΦLC2, respectively, ifnecessary. Further, the longitudinal axis 10 of the molecule of liquidcrystal is oriented in the same direction as that of rubbing due to analignment control film.

[0092] Secondly, the configuration and the principle of operation of aliquid crystal display panel of the horizontal electric field type willbe explained with reference to FIGS. 4(a) to 4(c).

[0093] FIGS. 4(a) and 4(b) are side-sectional views each showing onepixel portion of the liquid crystal display panel of the horizontalelectric field type, and FIGS. 4(c) and 4(d) are front views thereof. Inthese figures, active elements are not shown, except for a gateinsulating film 2. FIGS. 4(a) and 4(c) each show a state in which avoltage is not applied. Stripes of electrodes 1,3 and 4 are formedinside a pair of substrates 7, and alignment control films 5 are formedon those electrodes and substrates. In addition, polarizers 8 areprovided outside the substrates 7, and the transmitting axes thereof areshown in FIG. 4(c). Although the liquid crystal composite is sandwichedbetween the alignment control films 5, only the liquid crystal molecules6 are shown in the figures. In this example, it is assumed that thedielectric anisotropy of the liquid crystal molecules is positive.

[0094] The molecules of liquid crystal are alignment-controlledaccording to a rubbing direction 10 of the alignment control film 5 whena voltage is not applied.

[0095] The angle ΦLC is controlled so as to satisfy the relation,45°<|ΦLC|≦90° in consideration of the dielectric positive anisotropy. Inthis example, the directions of alignment of the molecules of the liquidcrystal on the upper and lower boundary surfaces are parallel to eachother, namely, ΦLC1=ΦLC2.

[0096] When a voltage with a predetermined polarity is applied, and thusan electric field 9 is produced, the molecules of liquid crystal changetheir directions to align with the direction of the electric field 9, asshown in FIGS. 4(b) and 4(d). As a result, the transmittance of lightcan be controlled according to the magnitude of the applied voltage,with respect to the transmitting axis of the polarized light of thepolarizer 8, and thereby information can be displayed on the liquidcrystal display panel.

[0097] This operation may be normally performed even if the compositionof the liquid crystal has a negative dielectric anisotropy. In thiscase, it should be noted that the state of original alignment must beset to 0°<|ΦLC|≦45°.

[0098] Referring now to FIG. 1, there is shown a schematic diagram ofthe liquid crystal display apparatus according to the present invention.The display apparatus is provided with an illuminant in the form of anedge light type back light unit having a light source 30, a wave guide32, a diffuser 33 and a prism sheet 34. The light source 30 has a colortemperature of 5885K and the luminescence spectrum shown in FIG. 7(a).

[0099]FIG. 9(a) shows the spectral transmittance of this liquid crystaldisplay panel when a drive voltage is applied, and FIG. 9(b) shows aluminescence spectrum obtained by using the above light source. A powerof 1.8 Watts is consumed in the light source unit. Further, FIG. 10shows the chromaticity coordinates concerning the above construction.The liquid crystal display panel uses a color of the cold color family.Fine white balance can be obtained by combining the display panel havinga light source with a lower color temperature.

[0100] A nematic liquid crystal composition is inserted between thesubstrates, of which the anisotropy of the dielectric constant ispositive, +9.0, and the anisotropy of the refractive index is 0.082 (589nm, 20° C.). The gap d between cells equals 3.8 μm. As a result,d_(LC)·Δn equals 0.31 μm, and d_(eff)·Δn equals 0.28 μm.

[0101] The liquid crystal display apparatus may also be provided with anedge light type back-light unit using a cold cathode fluorescent lamp asa light source having a color temperature of 11000K and the luminescencespectrum shown in FIG. 8(b).

[0102]FIG. 11A shows the spectral transmittance of this liquid crystaldisplay panel when a drive voltage is applied, and FIG. 11B shows aluminescence spectrum obtained by using the above light source. Further,FIG. 12 shows chromaticity coordinates concerning the aboveconstruction. In case of the combination of a yellowish liquid crystaldisplay panel and a light source with a color of the cold color family,a power of 2 Watts is consumed in the light source unit.

[0103] When the light source is changed to an edge light type back-lightunit with a color temperature of 5885K, a power of 1.8 Watts is consumedin the light source unit. FIG. 13A shows a luminescence spectrumobtained by using this light source, and FIG. 13B shows chromaticitycoordinates concerning this construction. In accordance with thisexample, it is possible to obtain a visually yellowish displayapparatus.

[0104] A color filter 24 is provided on the substrate opposite to thesubstrate having transistor elements, as shown in FIG. 6.

[0105] In one example, a nematic liquid crystal composition is insertedbetween the substrates, of which the anisotropy of the dielectricconstant is positive, +7.3, and the anisotropy of the refractive indexis 0.074 (589 nm, 20° C.). The gap d between cells equals 3.2 μm in sucha state that spherical polymer beads are scattered and sandwichedbetween the substrates and the liquid crystal is sealed in. As a result,d·Δn equals 0.24 μm. FIG. 14A shows the spectral transmittance of thisliquid crystal display panel when a drive voltage is applied, and FIG.14B shows chromaticity coordinates concerning the liquid crystal displayapparatus including a light source. The chromaticity coordinate underthe application of a drive voltage is positioned around standard lightsource C. A power of 1.8 Watts is consumed in the light source unit.According to this example, it is possible to obtain a liquid crystaldisplay apparatus of the horizontal electric field type, which issuitable for a color display.

[0106] In another example, a nematic liquid crystal composition isinserted between the substrates, of which the anisotropy of thedielectric constant is positive, +9.0, and the anisotropy of therefractive index is 0.082 (589 nm, 20° C.). The gap d between cellsequals 3.7 μm in such a state that spherical polymer beads are scatteredand sandwiched between the substrates and the liquid crystal is sealedin. As a result, d_(LC)·Δn equals 0.30 μm, and d_(eff)·Δn equals about0.27 μm. A phase plate is attached between the upper substrate and thepolarizer, so that the angle ΦF1 of the optical axis may become parallelwith the upper substrate, in other words, ΦF1 =ΦP1=75°. The phase plateis made of poly carbonate and has a retardation of 595 nm (550 nm). Theliquid crystal display panel is provided with an edge light typeback-light unit using a cold cathode fluorescent lamp as a light source.The light source has a color temperature of 4348K and the luminescencespectrum shown in FIG. 8(a).

[0107]FIG. 15 shows a trail appearing on the chromaticity coordinateswhen the voltage of the liquid crystal display apparatus is switchedfrom ON to OFF. The trail approaches a light source C. A power of 1.7Watts is consumed in the light source unit.

[0108] A striped color filter 24 with three colors, R, G, B, is providedon the substrate 7 opposite to the substrate having transistor elements,as shown in FIG. 6. A surface flattening protection film 25 is providedon the color filter 24, and the alignment film 5 is formed on theprotection film 25. A phase plate is attached between the substrate andthe polarizer, so that the angle ΦF1 of the optical axis may becomeorthogonal to the upper polarizer, in other words, ΦF1=ΦP2=−15°. Thephase plate is made of poly carbonate and has a retardation 349 of nm(550 nm). The liquid crystal display panel is provided with an edgelight type back-light unit using a cold cathode fluorescent lamp as alight source. The light source has a color temperature of 4703K and aluminescence spectrum as shown in FIG. 7(b). The chromaticitycoordinates when a drive voltage of the liquid crystal display apparatusis applied is close to the light source C. A power of 1.75 Watts isconsumed in the light source unit.

[0109] The thickness of the film of the color filter was about 2 μm atthe B and G pixels, and about 2.5 μm at the R pixels. The differencebetween these thicknesses remains as a level difference of about 0.3 μmafter spin-coating the flat film. The level difference represents thedifference of thickness between the liquid crystal layers. The edgelight type back light unit, which was used for the liquid crystaldisplay panel, included a cold cathode fluorescent lamp with a colortemperature of 4703K. FIG. 16 shows a voltage-transmittancecharacteristic of this liquid crystal display apparatus at wavelengthsof 615 nm, 545 nm and 465 nm, that is, the voltage-transmittancecharacteristic corresponding to each of the R, G and B pixels. It isseen from FIG. 16 that the characteristic of the transmittance of the Rpixels is shifted to the high voltage side. Accordingly, when the drivevoltage for the liquid crystal panel was applied, its transmittance hada characteristic in which red is suppressed. The white balance was finewhen the drive voltage was applied, and an electric power of 1.75 Wattswas consumed in the illuminant unit.

[0110] In another example, the thickness of the film of the color filterwas about 2 μm at the G and R pixels and about 1.5 μm at the B pixels.The thickness of the liquid crystal layer was about 3.8 μm at the G andR pixels, and about 4.1 μm at the B pixels. An edge light type backlight unit, which was used for the liquid crystal display panel,included a cold cathode fluorescent lamp with a color temperature of4703K. FIG. 17 shows a voltage-transmittance characteristic of thisliquid crystal display apparatus at wavelengths of 615 nm, 545 nm and465 nm, that is, a voltage-transmittance characteristic corresponding toeach of the R, G and B pixels. It is seen from FIG. 17 that thecharacteristic of the transmittance of the B pixels is shifted to thelow voltage side. Accordingly, when the drive voltage for the liquidcrystal panel was applied, its transmittance had a characteristic inwhich blue is emphasized. The white balance was fine when the drivevoltage was applied, and an electric power 1.75 Watts was consumed inthe illuminant unit.

[0111] In a further example, the thickness of the film of the colorfilter was about 2 μm at the G pixels, about 1.5 μm at the B pixels andabout 2.5 μm at the R pixels. The thickness of the liquid crystal layerwas about 4.2 μm at the G pixels, about 3.9 μm at the R pixels, andabout 3.9 μm at the B pixels. An edge light type back light unit, whichwas used for the liquid crystal display panel, included a cold cathodefluorescent lamp with a color temperature of 4348K. FIG. 18 shows avoltage-transmittance characteristic of this liquid crystal displayapparatus at wavelengths of 615 nm, 545 nm and 465 nm, that is, thevoltage-transmittance characteristic corresponding to each of the R, Gand B pixels. It is understood from FIG. 18 that the characteristic ofthe transmittance of the B pixels is shifted to the low voltage side,and the characteristic of the transmittance of the R pixels is shiftedto the high voltage side. The white balance was fine when the drivevoltage was applied, and an electric power 1.7 Watts was consumed in theilluminant unit.

[0112] In a still further example, the thickness of the film of thecolor filter was about 2 μm at the G and R pixels, and about 1.5 μm atthe B pixels. The thickness of the liquid crystal layer was about 4.5 μmat the G and R pixels, and about 4.2 μm at the B pixels. A phasedifference film made of poly-carbonate, which has a retardation of 997nm (550 nm), was inserted between the upper substrate and the polarizer,and it was attached so that the angle ΦF1 of its delay-phase axis wasparallel with the upper polarizer, that is, ΦF1=ΦP1=75°. An edge lighttype back light unit, which was used for the liquid crystal displaypanel, included a cold cathode fluorescent lamp with a color temperatureof 4348K. FIG. 19 shows a trail appearing on the chromaticitycoordinates. It is seen from FIG. 19 that the trail approaches thestandard illuminant C as a voltage is applied. The white balance wasfine when the drive voltage was applied, and the electric power 1.70watts was consumed in the illuminant unit.

[0113]FIGS. 20 and 21 show two different kinds of liquid crystal displaypanel of the horizontal electric field type. These figures each show afront view seen from a direction perpendicular to the surface of thesubstrate, while FIGS. 20(a) and 21(a) show side-sectional views takenalong the line A-A′ and FIGS. 20(b) and 21(b) show side-sectional viewstaken along the line B-B′ in FIGS. 20 and 21, respectively. A glasssubstrate is not shown.

[0114] In these figures, reference numeral 14 designates a thin filmtransistor, which has pixel electrodes (source electrodes) 4, signalelectrodes (drain electrodes) 3, a scanning electrode (gate electrode)12, and amorphous silicon 13. A common electrode 1 and the scanningelectrode 12 are formed by patterning the same metal layer formed on theglass substrate. The signal electrodes 3 and the pixel electrodes 4 areformed by patterning the same metal layer formed on a gate insulatinglayer 2. A load capacitance 16 is formed by allowing the insulatinglayer 2 to sandwich between the pixel electrodes 4 and the commonelectrode 1.

[0115] In FIG. 20, the pixel electrodes 4 are arranged between twocommon electrodes 1. An alignment control film 5 is provided directly onthe gate insulating layer 2, which has also the function of asurface-flattening film. In this case, the pitch between the pixels is69 μm in a horizontal direction and 207 μm in a vertical direction.

[0116] The width of each electrode is determined as follows.

[0117] In the electrodes used as a wiring electrode bridging a pluralityof pixels, that is, the scanning electrode 12, the signal electrode 3and the wiring portion (parallel with the scanning electrode, and in ahorizontal direction in FIG. 20) of the common electrode 1, the width ofthose electrodes are set to be, for example, 14 μm to avoid a wiredefect.

[0118] The width of the pixel electrode 4 formed independently for eachpixel and the longitudinally extending portion of the common electrode 1are respectively set to be 9 μm. The common electrode 1 and the signalelectrode 3 are partially superposed on each other (by 1 μm) through theinsulating layer. Thereby, it becomes unnecessary to provide a blackmatrix in a direction parallel with the signal electrode 3. Accordingly,there is provided only a black matrix 22 which can shield the light inthe direction of the scanning electrode. In addition, a color filter 24is provided only on the surface of one substrate.

[0119] While the black matrix 22 is provided on the substrate in whichthe electrodes are formed, it may be possible to provide the blackmatrix on the opposing substrate. These electrodes can be formed in aconventional way.

[0120] In the example of FIG. 21, the common electrodes 1 and the pixelelectrodes 4 are formed like a comb, in which two pixel electrodes 4 arearranged between three common electrodes 1. The pitch between the pixelsis 100 μm in a horizontal scanning direction and 300 μm in a verticaldirection. The insulating layer is provided on the portion where thecommon electrodes 1 and the signal electrodes 3 are superposed. Thethickness of the insulating layer is 2 μm.

[0121] Further, a surface-flattening insulating layer 27 is providedbetween the alignment control film 5 and gate insulating layer 2. Thematerial for the surface-flattening insulating layer 27 is SiO2 or SiN,the same as the gate insulating layer 2. However, it may be possible touse other suitable materials.

[0122] The width of each electrode is determined as follows.

[0123] In the electrodes used as a wiring electrode bridging between aplurality of pixels, that is, the scanning electrode 12, the signalelectrode 3 and the wiring portion (parallel with the scanningelectrode, and in a horizontal direction in FIG. 20) of the commonelectrode 1, the widths of those electrodes are set to be 10 μm, 8 μmand 8 μm, respectively, to avoid a wire defect.

[0124] The width of the pixel electrode 4 formed independently for eachpixel and the longitudinally extending portion of the common electrode 1are set to be 5 μm and 6 μm, respectively.

[0125] Because the width of the electrode is narrow in this example, thepossibility of breaks is increased due to the mixing of foreignparticles. In FIG. 21, a black matrix 22 is provided on the opposingsubstrate, along with the color filter 24, as shown in FIG. 22.Reference numeral 25 designates a protecting and surface-flatteninglayer. It is also possible to provide a color filter 24 on the opposedsubstrate or the substrate in which electrodes are formed. Theseelectrodes can be formed in a conventional way.

[0126]FIG. 23 shows one example of a driving circuit for the liquidcrystal display apparatus. In the driving circuit, a driving LSI isconnected to the active matrix type liquid crystal display panel 23.Scanning line driving circuits 20, signal line driving circuits 21 andcommon line driving circuits 26 are provided on a TFT substrate on whicha plurality of electrodes are mounted.

[0127] A scanning signal voltage, an image signal voltage and a timingsignal are supplied from a power circuit (not shown) and a controller19, and then the display operation responsive to the active matrix driveis started.

[0128] Embodiments of the present invention will be explainedhereinafter.

[0129] In FIG. 24, reference numeral 7 designates two substrates made ofglass plates having a thickness of 1.1 mm. A thin film transistor isformed on one of the substrates (lower substrate in FIG. 24), and thenan insulating layer 2 and an alignment film 5 are formed on the surfacethereof. In this embodiment, polyimide is used for the alignment film,and a rubbing-processing is performed to align the liquid crystal. Analignment film is also formed on the other substrate (upper substrate inFIG. 24) and then rubbing-processing is performed. The directions of therubbing at the upper and lower substrates are in parallel with eachother and at an angle of 75° with respect to the direction of theapplied voltage, that is, ΦLC1=ΦLC2=75°.

[0130] A nematic liquid crystal composition is inserted between thesubstrates 7, of which the anisotropy of the dielectric constant ispositive, +12.0, and the anisotropy of the refractive index is 0. 079(589 nm, 20° C.). The gap d between cells equals 3.02 μm due to the factthat spherical polymer beads are scattered and sandwiched between thesubstrates and the liquid crystal is sealed in. As a result, thethickness of the whole liquid crystal layer d_(LC) becomes equal to thegap d (3.02 μm). The value of d_(LC)·Δn (589 nm) equals 0.239 μm, andfrom the wavelength dependence characteristic of the anisotropy of therefractive index, d_(LC)·Δn (490 nm) equals 0.244 μm. As a result,d_(eff)·Δn (490 nm) equals about 0.22 μm.

[0131] The pair of substrates 7 are sandwiched by two polarizers 8. Thepolarization axis of one substrate is set to satisfy ΦP1=75°, and thepolarization axis of the other substrate is set to satisfy ΦP2=−15°.Thereby, the liquid crystal display panel 23 shown in FIG. 24 isobtained.

[0132] As shown in FIG. 24, a back-light unit, which is provided as anilluminant for transmitting light to the liquid crystal display panel23, comprises a fluorescent lamp 30, a light cover 31, a guide 32 and apolarizer 33, and has a color temperature of 5885K.

[0133] It may be possible to from the back-light unit by using aplurality of fluorescent lamps, and preferably, to provide a prism sheetbetween the polarizer 33 and the lower substrate 8.

[0134] In order to obtain a display closest to the achromatic color fromthe characteristics of the color of the liquid crystal display panel 23itself, except for the color filter, the color temperature of theilluminant is determined. Its color temperature is 5885K.

[0135] The spectrum characteristic of the back-light is shown in FIG.25, and the characteristic of the spectral transmittance in the lightstate of the liquid crystal display panel 23, except for the colorfilter, is shown in FIG. 26. In this embodiment, the dependence of thebrightness of the liquid crystal display apparatus on an applied voltageis shown in FIG. 27.

[0136] As seen from FIG. 26, the color shift due to the intensitycontrol is sufficiently suppressed in this embodiment.

COMPARISON EXAMPLE 1

[0137] A nematic liquid crystal composition is inserted between thesubstrates, of which the anisotropy of the dielectric constant ispositive, +9.0, and the anisotropy of the refractive index is 0.082 (589nm, 20° C.). The gap d between cells equals 3.83 μm.

[0138] In this comparison example, d_(LC)·Δn (589 nm) equals 0.310 μm,and d_(LC)·Δn (490 nm) equals 0.321 μm. As a result, d_(eff)·Δn (490 nm)equals about 0.30 μm. This value is out of the present invention.

[0139] This liquid crystal display panel is provided with an edge lighttype back-light unit using a cold cathode fluorescent lamp as a lightsource. The light source has a color temperature 6818K. Thecharacteristic of the spectral transmittance in a light state of theliquid crystal display apparatus without the color filter is as shown inFIG. 28, in which the transmittance in the short wavelength region isremarkably decreased. As a result, a trail appears on the chromaticitycoordinates until a voltage of the liquid crystal display apparatus isswitched from OFF (a dark state) to ON (a light state), as shown in FIG.29, in which the color is shifted and the liquid crystal display panelitself is colored.

[0140] As seen from the comparison example 1, the color is shifted asthe dark state is shifted into the light state in the liquid crystaldisplay apparatus using the liquid crystal display panel in which thetransmittance at the short wavelength is reduced. According to thiscomparison example, it is difficult to suppress the color shift in thecolor display and the coloring in the black and white display, and thusthe quality of the displayed image essentially deteriorates.

COMPARISON EXAMPLE 2

[0141] In the comparison example 2, a nematic liquid crystal compositionis inserted between the substrates, of which the anisotropy of thedielectric constant is positive, +9.0, and the anisotropy of therefractive index is 0.082 (589 nm, 20° C.). The gap d between cellsequals 4.26 μm.

[0142] In this comparison example, d_(LC)·Δn (589 nm) equals 0.345 μm,and d_(LC)·Δn (490 nm) equals 0.357 μm. As a result, d_(eff)·Δn (490 nm)becomes equal to about 0.33 μm. This value is also outside of thepresent invention. It is understood that the transmittance for bluelight is reduced.

[0143] This liquid crystal display panel is provided with an edge lighttype back-light unit using a cold cathode fluorescent lamp as a lightsource. The light source has a color temperature 6818K. A trail appearson the chromaticity coordinates until a voltage of the liquid crystaldisplay apparatus is switched from OFF (a dark state) to ON (a lightstate) as shown in FIG. 30. As seen from the comparison example 2, thecolor is shifted to a yellowish color, as the dark state is shifted intothe light state. Also, according to this comparison example, it isdifficult to improve the quality of the displayed image.

[0144] The change in the characteristics caused by the local change inthe thickness of the liquid crystal will be explained with reference tovarious embodiments and comparison examples.

[0145] Embodiment A

[0146] The liquid crystal display apparatus has two substrates, one ofwhich has a color filter with B, G and R pixels on its surface. Anematic liquid crystal composition is inserted between the substrates,of which the anisotropy of the dielectric constant is positive, +12.0,and the anisotropy of the refractive index is 0.079 (589 nm, 20° C.).The gap d between cells is formed by scattering spherical polymer beadsand sandwiching them between the substrates. The gap is adjusted tod=2.87 μm by selecting the radius of the beads.

[0147] In this comparison example, d_(LC)·Δn (589 nm) equals 0.227 μmand d_(LC)·Δn (490 nm) equals 0.232 μm. As a result, d_(eff)·Δn (490 nm)equals about 0.21 μm. This value is out of the present invention.

[0148] The liquid crystal display panel is provided with a back-lightunit as a light source which has a color temperature of 6818K.

[0149] Embodiment B

[0150] The liquid crystal display apparatus has two substrates, one ofwhich has a color filter with B, G and R pixels on its surface. Anematic liquid crystal composition is inserted between the substrates,of which the anisotropy of the dielectric constant is positive, +12.0,and the anisotropy of the refractive index is 0.079 (589 nm, 20° C.).The gap d between cells is formed by scattering spherical polymer beadsand sandwiching them between the substrates. The gap is adjusted tod=3.17 μm by selecting a radius of the beads which is different fromthat in embodiment A.

[0151] In this embodiment B, d_(LC)·Δn (589 nm) equals 0.250 μm andd_(LC)·Δn (490 nm) equals 0.256 μm. As a result, d_(eff)·Δn (490 nm)equals about 0.23 μm.

[0152] The liquid crystal display panel is provided with a back-lightunit as a light source which has a color temperature of 4703K.

COMPARISON EXAMPLE C

[0153] The liquid crystal display apparatus has two substrates, one ofwhich has a color filter with B, G and R pixels on its surface. Anematic liquid crystal composition is inserted between the substrates,of which the anisotropy of the dielectric constant is positive, +9.0,and the anisotropy of the refractive index is 0.082 (589 nm, 20° C.).The gap d between cells is adjusted to d=3.83 μm.

[0154] In this comparison example, d_(LC)·Δn (589 nm) equals 0.314 μm,and d_(LC)·Δn (490 nm) equals 0.321 μm. As a result, d_(eff)·Δn (490 nm)equals about 0.30 μm. This value is out of the present invention.

[0155] The liquid crystal display panel is provided with a back-lightunit as a light source which has a color temperature of 6818K.

COMPARISON EXAMPLE D

[0156] The liquid crystal display apparatus has two substrates, one ofwhich has a color filter with B, G and R pixels on its surface. Anematic liquid crystal composition is inserted between the substrates,of which the anisotropy of the dielectric constant is positive, +9.0,and the anisotropy of the refractive index is 0.082 (589 nm, 20° C.).The gap d between cells is adjusted to d=4.26 μm.

[0157] In this comparison example, d_(LC)·Δn (589 nm) equals 0.349 μm,and d_(LC)·Δn (490 nm) equals 0.357 μm. As a result, d_(eff)·Δn (490 nm)equals about 0.33 μm. This value is also out of the present invention.

[0158] The liquid crystal display panel in the comparison example D isprovided with a back-light unit as a light source which has a colortemperature of 6818K.

[0159] As should be clearly understand from the above description, thereis a difference of 10% in the gap between the embodiments A and B, andbetween the comparison examples C and D. Accordingly, it is possible toestimate the color shift caused by the change in the thickness d_(eff)(≈d) of the liquid crystal layer, that is, the gap margin.

[0160]FIG. 31 shows the characteristic of the color difference ΔEuv* inrelation to the applied voltage in the embodiments A and B, and thecomparison examples C and D. The characteristic of the color differencecan be obtained by using the color difference equation of the main colorfamily concerning L*u*v* proposed by CIE in 1976.

[0161] In general, the value of the color difference ΔEuv* allowable inthe same liquid crystal display panel is around 3 in such a liquidcrystal display apparatus.

[0162] Referring now to FIG. 31, as clearly understood from thecharacteristic shown by the solid line of this figure, even if there isa difference of 10% in the gap between the embodiments A and B in thesame display panel, the value of the color difference ΔEuv* is held toless than 2. Accordingly, a color defect is not evident in this case.

[0163] While, as clearly understood from the characteristic shown by thedotted line of FIG. 31, if there is a difference of 10% in the gapbetween the comparison examples C and D in the same display panel, alarge color difference ΔEuv* appears in response to the applied voltage.Therefore, a remarkable color defect may be expected in this case.

[0164] In the embodiments of the present invention, it is understoodthat even if there is a difference of 10% in the gap between theembodiments A and B in the same display panel, a color defect is notevident in this case, and it is possible to obtain a sufficient marginfor the change in the gap.

[0165] The reason for the occurrence of a color difference in theembodiments of the present invention and the comparison examples will beexplained from the view point of the difference in the passingcharacteristic for the colors, R, G and B.

[0166]FIGS. 32 and 33 show the characteristics of the brightness inrelation to the applied voltage in the embodiments A and B by settingeach of the colors R, G and B as parameters. Further, FIGS. 34 and 35show characteristics similar to those of FIGS. 31 and 32 with regard tothe comparison examples C and D, where the value of the wavelength ofeach color was measured by using the back-light with the luminescencecharacteristic shown in FIG. 25. The value of the wavelength of B (blue)was set to the middle value, 465 nm, of the spectra in a blue portion.

[0167] The following fact is clarified from these figures.

[0168] In the embodiments of the present invention shown in FIGS. 32 and33, the tendency of the change in the characteristic of each color isthe same until the display is switched from a dark state to a lightstate, and the contribution of a color to the brightness is almost equalin each color. Accordingly, the color shift is not evident in theseembodiments.

[0169] In the comparison examples, the tendency (shown by a solid line)of the change in the characteristic of blue is different from those ofred and green. As the applied voltage increases, the contribution ofblue to the brightness decreases. Accordingly, in these examples, as thebrightness increases, the component of blue is reduced. As a result, ayellowish display appears, and thus the color is shifted.

[0170] In FIG. 36, the passing ratio of each wavelength in the lightdisplay is expressed in terms of the brightness by setting theretardation d_(eff)·Δn (μm) as a parameter. As seen from FIG. 36, thebrightness in the short wavelength region (blue region) less than 500 nmextremely changes and is remarkably reduced by a small change in theretardation d_(eff)·Δn.

[0171] It is important to maintain the relationship of the transmittancebetween the three wavelengths of the colors R, G and B to apredetermined state.

[0172] The predetermined state refers to a state wherein thetransmittance in the wavelength of the longest wave among the spectracorresponding to blue of the emission spectra of the back-light isalways larger than that in the wavelengths 545 nm (green) and 630 nm(red).

[0173] Accordingly, The present invention must satisfy the conditionthat the above relationship is always maintained.

What is claimed is:
 1. A liquid crystal display apparatus comprising aliquid crystal panel having a pair of substrates, a plurality ofelectrodes formed on at least one of said pair of substrates and aliquid crystal layer sandwiched between said pair of substrates, and alight source provided on one surface of said liquid crystal panel,wherein an electric field in said liquid crystal layer produced by saidplurality of electrodes is predominantly in parallel with surfaces ofsaid pair of substrates, and wherein said light source has a luminouscharacteristic with a first chromaticity and said liquid crystal panelhas a characteristic of spectral transmittance with a secondchromaticity different from the first chromaticity so as to compensatefor the color of said light source.
 2. A liquid crystal displayapparatus according to claim 1, wherein the first chromaticity is one ofa warm color family and a cold color family and the second chromaticityis the other of the warm color family and the cold color family.